Page 110 - Handout Computer Network.

5.3.1 Path Determination

Path determination occurs at Layer 3 (the network layer). It lets a router evaluate the available
paths to a destination and establish the preferred handling of a packet.
Routing services use network topology information when evaluating network paths, as shown
in Figure 5-3.

Path determination is the process that a router uses to choose the next hop in a path toward
a packet’s ultimate destination.

This process is also called routing the packet.

Figure 5-3 shown a Choosing a Path Process

Path determination for a packet can be compared to a person driving a car from one side of a
city to another. The driver has a map that shows the streets to take to get to the destination. The
drive from one intersection to another is a hop.
Similarly, a router uses a map that shows the available paths to a destination. Routers can also
make their decisions based on the traffic density and the link’s speed (bandwidth), just as a driver
might choose a faster path (a highway) or use less-crowded back streets. In this section, you’ll see
how a router determines the best path for packets traveling from one network to another.

5.3.2 Network Layer Addressing

A network address helps the router identify a path within the network cloud and also provides
hierarchical or subnet information. The router uses the network address to identify the destination
network of a packet within an internetwork.
In addition to the network address, network protocols use some form of host, or node,
address. For some network layer protocols, a network administrator assigns host addresses according
to some predetermined network addressing plan.

For other network layer protocols, assigning host addresses is partially or completely dynamic
or automatic. Figure 5-4 shows three devices in Network 1 (two workstations and a router), each with

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